The invention relates to improvements in exhaust gas recirculation devices for use diesel fuel injected engines. In a known apparatus of this kind, closed-loop control of the fuel-air ratio is provided, wherein the guide value is the induced air quantity, variable by means of a throttle valve, as measured by an air flow rate meter. The initial value of the air flow rate meter is divided, in a closed-loop control device, by the rpm measured in a fuel injection pump. The value thus attained is compared with a control value, which corresponds to the position of the quantity-adjusting device of the fuel injection pump and represents a value for the fuel injection quantity. The position of the quantity-adjusting device of the fuel injection pump is corrected by means of a final control element on the basis of the amount of deviation from the two control values. The throttle valve here, by its position, also affects the quantity of recirculated exhaust gas which is available, when the induced air quantity is throttled, to make up the remaining filling of the cylinders of the internal combustion engine.
This apparatus is very expensive, and it performs its control function relatively slowly, because if there is a change in the position of the throttle valve the desired values are established only after the elapse of the dead time of the control loop. In particular, there is the danger that because of an excessively large quantity of recirculated exhaust gas, there may briefly be heavy soot formation.